Yes, I quoted that from page 5 of today's previews. All Ruins are Actions.
You wrote that all Shelters were Actions.
I agree with the theory that one of the. Is going to be beneficial.
I also don't get why people think one will will be +action. That doesn't do anything. I also don't see why people think it will be these boring vanilla cards (+card, +coin, and so on.)
My guesses
A card with -1 victory point but is a cantrip like a reverse great hall
If this card is trashed, you must trash another card of cost 3 or more with it. If you can't, draw another ruin.
Or
If you trash this card, gain a card from the trash
They are expected to be boring vanilla because Ruined Market is such, and Donald X commented that we should be able to predict the three others, thus +1 action, +1 card and +$1 are likely. I agree that +1 action pretty much does nothing, but it would still work, sort of. It has interaction with Conspirator, HoP, draw-to-X cards like Library. So there's that. (PPE: ninja'd)
I don't think that anything is going to be actually beneficial. I mean, Ruined Market can be beneficial sometimes, sure, but most of the time it will be a hindrance. I expect the same of the other ruins, because otherwise it is way too swingy. It is already a bit swingy in that some Ruins will be better than others, but I expect that their usefulness will still be pretty close together on the lower end of things.